Patterns of resistance of inbred mice to Trypanosoma cruzi are determined by parasite strain.

Host response and parasite behavior of three different T. cruzi strains (I-Peruvian, II-21SF, III-Colombian) were investigated by evaluating the course of infection in six inbred strains of mice (A/J, AKR, C3H/He, BALB/c, C57BL/10, DBA/1). Resistance was evaluated in terms of the harmonic mean survival time and the infection was monitored by parasitemia, histopathology and immunological parameters (immunoglobulin subclass levels and antibody titers). All six mouse strains showed high susceptibility to the Peruvian strain (Type I). However, they displayed a different spectrum of susceptibility to Types II and III. Each T. cruzi strain maintained its basic features in the different mouse strains. Despite different maximum levels, the parasitemic curves were characteristic for each type of T. cruzi strain. There was a correlation between the degree of resistance of strains DBA and B10 and their high levels of IgG2a and IgG2b, as well as the presence of the H-2d haplotype, indicating that the genetic background of the mice is also important. The inflammatory process varied with each mouse strain and was correlated with the levels of IgG2a, with resistant mice showing predominance of neutrophilic infiltration with a rise in IgG2a. The susceptible strains responded with a mild inflammatory process with predominance of mononuclear cells. These data suggest that the parasite strain is the most important factor determining the resistance of the different mouse strains to infection with T. cruzi.